I. Field of the Invention
The present invention relates to a method of evaluating the dimension accuracy of patterns such as photoresist patterns and etching patterns formed during the process of manufacturing semiconductor devices, for example. The present invention also relates to a photomask used for the method.
II. Description of the Prior Art
Photo-engraving process is a technique widely used in the process of manufacturing various kinds of semiconductor devices. This technique includes a step of exposing to light a photoresist layer formed on a semiconductor substrate through a photomask which has a desired pattern to be formed. When the photoresist layer exposed to light is developed, a resist pattern is obtained corresponding to the pattern of the photomask. Layers such as Si or SiO.sub.2 under the resist pattern are etched with appropriate etching means using the resist pattern as a mask, then a pattern etched as desired is obtained.
It is extremely important for the high precision of semiconductor device that the dimension of pattern formed by the photo-engraving process is just as set. It becomes therefore necessary to evaluate the measure precision of photoresist pattern and/or etched pattern formed by the photo-engraving process.
The micrometer (or microscope) has been widely used to measure the dimension of pattern. In the case of this method, however, the dimension to be measured becomes different depending upon the manner of focusing the microscope. Therefore, this method causes measuring error to be made large and is far from establishing absolute evaluation of pattern dimension.
Alternative is to measure the dimension of pattern in such a way that a sample is subjected to laser beam and its reflected beam is monitored. However, values measured according to this method are substantially influenced by the sectioned contour of the object to be measured. This method is therefore suitable for measuring relative dimension but not for measuring absolute dimension.
There are many other methods of measuring the dimension of pattern but they are not necessarily satisfactory. A method of most accurately measuring absolute dimension is achieved using the scanning electro-microscopy (SEM). However, this method makes it necessary to prepare a measuring sample and causes the in-process monitoring of pattern to be made troublesome and complicated.